How to Plant Onions at Home: Basic Growing Guide

If you’re planning on adding onions to your vegetable garden, that’s a good idea. Many beginner gardeners find them easy to grow.

Onions usually take about 90 to 120 days to mature when grown from seed, depending on the variety.

In most climates, the best time to plant them is in early spring to mid-spring. For those living in warmer climates, autumn is a good time to plant.

Transplant the seedlings when they are mature enough. Onions grow best in full sun and need at least 6 to 8 hours of direct sunlight each day.

Below is a basic guide on how to grow onions at home:

How to Grow Onions from Seed

Choose an onion variety that matches your area. Short-day onions grow best in warm southern climates, while long-day onions are better for cooler northern regions [1].

Start the seeds indoors in a container with rich compost or potting soil. However, it’s best to start them 8 to 10 weeks before you plan to transplant them outdoors into the garden.

You can soak the seeds in water for a few hours before planting to help speed up germination. Follow the instructions on the seed packet, as recommendations may vary.

Keep the soil moist and place the container in a warm area until the seeds sprout. Once they sprout, place the container in a cool, well-lit area.

Growing From Scraps

Growing onions from scraps is a fun way to regrow a plant.

In fact, onions are one of the easiest vegetables to grow from scraps [2]. However, the new bulbs may be smaller, and some varieties are better for growing green onions than large storage bulbs.

• Cut off the root end, then use toothpicks or other materials to hold the scraps in place over a cup or bowl.
• Next, fill the dish, jar, or container with water and suspend just the root end in the water.
• Soon you’ll see tiny sprouts growing from the top and new roots growing from the bottom.
• Afterward, place the sprouted scrap in the ground or a pot, covering it until just the sprouts are above the soil line.
• Finally, water, fertilize, and care for it just like an onion grown from seed or set.

Another source says to regrow onions from scraps; just cut off the root end and plant it directly in moist soil in a sunny location.

Planting Onion Sets

Onion sets are miniature bulbs that usually grow into full-size onions in about 60 to 90 days.

These are tougher than seedlings and grow much faster than seeds. Plant onion sets about 3 to 4 inches apart. Space rows 12 to 18 inches apart.

Do not bury them more than an inch deep in the soil. Some gardeners also soak onion sets in compost tea or plain water before planting, although this step is optional.

Additionally, when picking up bulbs at a nursery, check that they are dry (typically sold in mesh bags) and firm.

Spacing

Spacing will depend on whether you are planting onions from seedlings or sets.

When transplanting, space the seedlings about 6 inches apart. Closer spacing will produce smaller bulbs. The rows should also be about 12 inches apart.

When planting sets, plant them about 3 to 4 inches apart. Also, add straw mulch between sets and in between the rows. Allow for 12 to 15 inches of spacing between rows.

How Deep to Plant?

Sow seeds a quarter-inch deep in the soil. If planting from sets, place them approximately 1 inch deep in the soil so they can take root.

Planting depth is usually the same for most onions. However, the best planting time depends on your climate and onion variety.

Watering

For onion plants to produce high yields, they need adequate water. Therefore, provide about an inch of water per week.

Also, it is best to use mulch around the plants, as it will help keep the soil moist and weed-free.

Reduce watering as the bulbs finish growing, and the tops begin to fall over. This helps the onions cure more evenly and reduces the risk of rot.

Mulching

Keep weeds under control, because onions do not compete well with them for water and nutrients.

Spread 2 to 3 inches of straw or shredded leaves around the plants. Mulch helps keep the soil moist, reduces weeds, and keeps the bulbs clean.

Fertilizer Requirements

To grow well, onions require rich, fertile soil that drains well. Therefore, mix compost into the soil before planting.

Once the plants are growing well, feed them with a nitrogen-rich fertilizer every few weeks until the bulbs begin to form [3].

Onions also need phosphorus and potassium for healthy root and bulb development. Adding compost around the plants during the growing season can also improve the soil.

Growing in Containers

You can grow onions in shallow containers at least 8 inches deep, either from sets or seeds.

• Fill the container with potting soil, leaving about 1 inch of space at the top for watering.
• Mix compost into the potting soil before planting. You can also add a thin layer of compost around the plants as they grow.
• Cover the onion set with about 1 inch of soil when planting. As the bulb grows, it may naturally push above the soil surface. This is normal.
• Do not trim healthy leaves. The leaves help the bulb grow larger.

Onion Companion Plants

Anything in the cabbage family makes a great companion plant for onions.

The strong smell of onions may help discourage pests such as carrot flies and aphids, so they are often planted near crops that are commonly attacked by these pests.

Lettuce and carrots are also good options. They have very different root systems that won’t compete with onions for the same soil resources. Tomatoes, lettuce, and strawberries are other great companions for onions.

However, avoid all varieties of peas and beans, as they do not grow well near onions.

Harvesting

How can you tell when onions are ready to harvest?

When most of the leaves turn yellow and fall over, the onions are ready to harvest. However, if any plants produce flower stalks, harvest them as soon as possible.

When harvesting, gently loosen the soil with a garden fork if needed, then pull the onions from the ground. Next, shake the dirt off around the bulbs.

Finally, let the onions dry in a warm, well-ventilated place for several days to cure. If the weather is dry, you can leave them in the garden for a day or two before moving them under cover.

Pests and Diseases

• The onion fly is one of the most common pests that affects the allium family. They lay eggs, and the maggots hatch and feed on the seedlings. This fly resembles the housefly.
• The lesser bulb fly looks similar but is smaller. Once infected, the plants must be dug up and destroyed.
• Thrips lay eggs on onion leaves. After hatching, both the young insects and adults feed by sucking sap from the leaves.

Overwatering or poor drainage can encourage diseases that cause leaf spots, bulb rot, and other problems. Onion plant diseases include soft rot, purple blotch, damping off, downy mildew, and onion smut.

Storing

Store onions in a dry, cool place. If they are too moist or warm, resprouting can occur.

Mesh bags, baskets, or cardboard boxes with holes help keep onions dry and allow good airflow during storage.

Properly cured onions can last for several months in a cool, dry, well-ventilated place. Sweet onions usually have a shorter storage life than storage varieties.

See also: How to Plant Garlic: A Basic Growing Guide.

Takeaway

Growing your own onions can be rewarding and give you a fresh harvest to enjoy. Whether you start with seeds or sets, good soil, water, and sunlight will all affect how well your onions grow.